All I've ever seen are basically guesses that fall within the range that STIHL mentioned. Gaile recently mentioned that there are 11 million accounts I think, but that would include dormant and duplicate accounts as well as f2ps, if the number was even a serious reference and not hyperbole . . .

But the answer doesn't even really matter that much, what's really impt is whether there are ppl doing the things you want to do when you need them to do them, and as far as I've seen there are pretty much always at least that many ppl playing

No, you count as 2 players, just like anyone else with multiple accounts...as far as I'm concerned, any account that is logged onto is a player(even if one person logs onto 20 accounts, that's 20 players, but I'm sure not many others like my method of math).

Yes...no...maybe...what do you want, can't you see I'm busy saving the world...AGAIN!

Only Anet knows and they're not telling. A few years ago official sources said there were 11 million accounts - but of course not all of them are active.

Even for Anet it may not be a straight-forward question to answer. You could do a simple measure like how many accounts are logged into per month - but then you'd be counting my second account where I literally just log in, collect the daily login reward and close the game which I doubt most people would consider playing the game. And you'd usually miss my old guild leader who logs in only when there's a new release but then is online for nearly 8 hours a day until he's done everything he wants, then stops again.

I suspect they probably use a few different measures - probably things like number of unique logins per day/week/month, maximum concurrent logins, average play time, gems purchased per account, real money spent per account etc. Most of these could either be an average or a chart, which would probably be a bell curve. I've heard they can also do more detailed info too, like "heat maps" which show where in the game players spend the most time.

But as other people said most of that isn't important for us. What we need to know is whether there's enough people around for the things we want to do, and for things like maintaining supply and demand on the trading post. Answers will vary between people (I imagine if you're looking for new people to fight at the top of ranked PvP the active population seems a lot smaller than if you're looking for people to do world bosses for example) but in general I think the answer is yes - allowing for busy and quiet times of day there are enough people in-game for whatever you want to do.

"You can run like a river, Till you end up in the sea,
And you run till night is black, And keep on going in your dreams,
And you know all the long while, It's the journey that you seek,
It's the miles of moving forward, With the wind beneath your wings."